This invention relates to appliance timers and, particularly, to an appliance timer having a timing cam which operates a series of switches for operating circuits controlled by the timer. The timer includes an improved motor assembly for driving the timing cam which greatly reduces the size of the timer assembly and its complexity.
Although the principles of the present invention may be included in various timers, a particular application is made in timers of the type employed to control the various circuits and functions of automatic laundry appliances, such as washers and dryers. Appliance timers basically comprise a rotatable member having a plurality of projecting cams which sequentially engage switch members which, in turn, control the various operations of the appliance.
Basically, there are two types of timers for home appliances. One such time is a cylindrical rotary drum having a plurality of cams projecting from its surface which engage switch members and is quite similar to a music box. A principal disadvantage of such a timer is that it is bulky and it is difficult to mount the timer in the space requirements dictated by the appliance manufacturer. Another timer is set forth in U.S. Pat. No. 2,703,347 to A. R. Constantine, issued Mar. 1, 1975. According to that patent, the appliance timer comprises a flat disc mounted in a housing and having ratchet teeth on its periphery. The disc is driven incrementally about a central shaft by a pawl, which in turn is driven in a reciprocal manner by a synchronous motor. At least one face of the disc is provided with arcuate cam surfaces which are concentrically arranged about the face or faces of the disc. Switch members are arranged about the faces of the housing to engage the arcuate cam members upon rotation of the disc. Electrical connectors cooperate with the switch members to control the various cycles of the appliance.
In a timer having a rotary drum type cam, the synchronous motor is generally located in the timer housing so that its output shaft is parallel to the cam drum and has a gear train between its output shaft and the drum cam which comprises a speed reduction gear train to drive the drum at a very low rotational speed. This arrangement results in a construction wherein the length of the timer housing is at least equal to the diameter of the drum cam and the diameter of the synchronous motor. The depth of the housing is generally dictated by the axial extent of the drum cam.
While the depth of the timer housing according to the above-mentioned Constantine patent is considerably reduced because of the disc cam arrangement, the length and width of the housing are increased to accommodate the switches, the synchronous motor, and the pawl drive mechanism.
A further disadvantage of the prior art timers is that they are extremely difficult to service and reassemble by relatively unskilled repair personnel.